The invention relates to a method and an arrangement for operating an internal combustion engine.
Modern control systems are available for operating internal combustion engines and adjust the power of the engine in dependence upon input quantities by controlling the power parameters of the engine. Many different monitoring measures are provided for avoiding unwanted operating situations as a consequence of disturbances and especially because of the disturbances in the electronic control apparatus of the engine control. The monitoring measures ensure a reliable operation of the engine as well as the availability for use thereof. The monitoring of the control of an internal combustion engine on the basis of torque is shown in DE-A 195 36 038 (U.S. Pat. No. 5,692,472). There, a maximum permissible torque is determined at least on the basis of the accelerator pedal position. In addition, the actual torque of the engine is computed in dependence upon engine speed (rpm), ignition angle position and load (air mass, et cetera). The maximum permissible value is compared to the computed current value for monitoring. Fault reaction measures are initiated when the actual value exceeds the maximum permissible value. This monitoring strategy offers a reliable and satisfactory monitoring of internal combustion engines. However, it is based on the measured air mass supplied to the engine. The torque, which is determined from the measured air mass, does not correspond to the actual values in internal combustion engines which are operated at least in an operating state with a lean air/fuel mixture such as direct-injected gasoline engines or diesel engines. For this reason, the described monitoring strategy is useable only to a limited extent. In gasoline internal combustion engines having direct injection in stratified-charge operation, the detected air mass and the adjusted ignition angle are not adequate for computing the actual torque.
It is the object of the invention to provide a concept for monitoring the control of an internal combustion engine which is operated at least in some operating states with a lean air/fuel mixture.
A monitoring measure for gasoline direct-injected internal combustion engines is known from the non-published DE 197 29 100.7. There, the actual torque of the engine is determined on the basis of the combusted fuel mass and compared to a permissible maximum torque determined on the basis of the accelerator pedal position and a fault reaction is initiated when the actual torque exceeds the maximum torque.
For monitoring an internal combustion engine, which is operated in at least one operating state with a lean air/fuel ratio, it is known from U.S. patent application Ser. No. 09/554,128, filed May 9, 2000 to permit in at least one operating state only operation of the engine with an approximately stoichiometric or rich air/fuel ratio or only an operation with limited air supply and to then monitor the operation of the engine on the basis of at least one operating quantity thereof.
A further individual measure is shown in DE-A1 196 20 038. There, for monitoring a fuel metering system, a signal of a sensor, which detects the exhaust gas composition, is checked for deviations from a pregiven value.
All these individual measures show only solutions for individual problem points, that is, they limit the availability of use of the control system. A monitoring concept, which is satisfactory with the view to availability of use and completeness, is not described.
A procedure is described with permits a complete monitoring of the control of internal combustion engines which are operated in at least an operating state with a lean air/fuel mixture. In a reliable manner, an increase (which is impermissible with respect to the driver command) of the indicated engine torque of such an engine is avoided as a consequence of a software defect or a hardware defect. The indicated engine torque is the torque of the engine which is generated directly by the combustion of the air/fuel mixture. The torque, which is outputted by the engine, is computed therefrom while considering loss torques and consumer torques.
It is especially advantageous that the accuracy of the monitoring is improved because not the air flowing over the throttle flap is used as indicator for the indicated torque but the fuel mass injected into the cylinder. This fuel mass is the quantity determining torque in lean and stoichiometric operating conditions.
It is especially advantageous when the fuel mass, which is injected into the cylinder, is determined from the injection time or possibly even only in specific operating states when the fuel mass, which is injected into the cylinders, is determined from the air mass, which is supplied to the engine, and the exhaust-gas composition. In specific operating states, a monitoring on the basis of a quantity for the exhaust-gas composition such as a measure for the oxygen content, , can take place as an additional measure for monitoring the engine. This additional measure secures the torque monitoring and thereby further improves the same.
Further, the input of a trace of the permissible torque in dependence upon at least one of the quantities: engine speed, engine temperature and driver command (accelerator pedal position) is advantageous for which driver command, at very small pedal angles, a maximum permissible torque is less than the zero load and wherein a permissible torque up to maximally zero load is assigned for mean pedal angles and wherein a maximum permissible torque is assigned in accordance with a pregiven relationship to large pedal angles. In this way, a satisfactory response of the torque monitoring is achieved when there is a fault.
It is further advantageous that special operating states can be considered during monitoring such as active measures for catalytic converter protection, catalytic converter heating and/or methods for holding the catalytic converter warm.